Isotopes of krypton

There are 34 known isotopes of krypton (₃₆Kr) with atomic mass numbers from 67 to 103. Naturally occurring krypton is made of five stable isotopes and one (⁷⁸
Kr) which is slightly radioactive with an extremely long half-life, plus traces of radioisotopes that are produced by cosmic rays in the atmosphere.

Isotopes of krypton (₃₆Kr)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct 78Kr 0.360% 9.2×1021 y[2] εε 78Se 79Kr synth 35 h β+ 79Br 80Kr 2.29% stable 81Kr trace 2.3×105 y ε 81Br 81mKr synth 13.10 s IT 81Kr ε 81Br 82Kr 11.6% stable 83Kr 11.5% stable 84Kr 57.0% stable 85Kr trace 10.728 y β− 85Rb 86Kr 17.3% stable
Standard atomic weight Ar°(Kr)
	83.798±0.002[3] 83.798±0.002 (abridged)[4]
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List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da)[5] [n 2][n 3]	Half-life[1] [n 4][n 5]	Decay mode[1] [n 6]	Daughter isotope [n 7][n 8]	Spin and parity[1] [n 9][n 5]	Natural abundance (mole fraction)
	Excitation energy							Normal proportion[1]	Range of variation
67Kr	36	31	66.98331(46)#	7.4(29) ms	β+? (63%)	67Br	3/2-#
					2p (37%)	65Se
68Kr	36	32	67.97249(54)#	21.6(33) ms	β+, p (>90%)	67Se	0+
					β+? (<10%)	68Br
					p?	67Br
69Kr	36	33	68.96550(32)#	27.9(8) ms	β+, p (94%)	68Se	(5/2−)
					β+ (6%)	69Br
70Kr	36	34	69.95588(22)#	45.00(14) ms	β+ (>98.7%)	70Br	0+
					β+, p (<1.3%)	69Se
71Kr	36	35	70.95027(14)	98.8(3) ms	β+ (97.9%)	71Br	(5/2)−
					β+, p (2.1%)	70Se
72Kr	36	36	71.9420924(86)	17.16(18) s	β+	72Br	0+
73Kr	36	37	72.9392892(71)	27.3(10) s	β+ (99.75%)	73Br	(3/2)−
					β+, p (0.25%)	72Se
73mKr	433.55(13) keV			107(10) ns	IT	73Kr	(9/2+)
74Kr	36	38	73.9330840(22)	11.50(11) min	β+	74Br	0+
75Kr	36	39	74.9309457(87)	4.60(7) min	β+	75Br	5/2+
76Kr	36	40	75.9259107(43)	14.8(1) h	β+	76Br	0+
77Kr	36	41	76.9246700(21)	72.6(9) min	β+	77Br	5/2+
77mKr	66.50(5) keV			118(12) ns	IT	77Kr	3/2−
78Kr[n 10]	36	42	77.92036634(33)	9.2 +5.5 −2.6 ±1.3×1021 y[2]	Double EC	78Se	0+	0.00355(3)
79Kr	36	43	78.9200829(37)	35.04(10) h	β+	79Br	1/2−
79mKr	129.77(5) keV			50(3) s	IT	79Kr	7/2+
80Kr	36	44	79.91637794(75)	Stable			0+	0.02286(10)
81Kr[n 11]	36	45	80.9165897(12)	2.29(11)×105 y	EC	81Br	7/2+	6×10−13[6]
81mKr	190.64(4) keV			13.10(3) s	IT	81Kr	1/2−
					EC (0.0025%)	81Br
82Kr	36	46	81.9134811537(59)	Stable			0+	0.11593(31)
83Kr[n 12]	36	47	82.914126516(9)	Stable			9/2+	0.11500(19)
83m1Kr	9.4053(8) keV			156.8(5) ns	IT	83Kr	7/2+
83m2Kr	41.5575(7) keV			1.830(13) h	IT	83Kr	1/2−
84Kr[n 12]	36	48	83.9114977271(41)	Stable			0+	0.56987(15)
84mKr	3236.07(18) keV			1.83(4) μs	IT	84Kr	8+
85Kr[n 12]	36	49	84.9125273(21)	10.728(7) y	β−	85Rb	9/2+	1×10−11[6]
85m1Kr[n 12]	304.871(20) keV			4.480(8) h	β− (78.8%)	85Rb	1/2−
					IT (21.2%)	85Kr
85m2Kr	1991.8(2) keV			1.82(5) μs	IT	85Kr	(17/2+)
86Kr[n 13][n 12]	36	50	85.9106106247(40)	Observationally Stable[n 14]			0+	0.17279(41)
87Kr	36	51	86.91335476(26)	76.3(5) min	β−	87Rb	5/2+
88Kr	36	52	87.9144479(28)	2.825(19) h	β−	88Rb	0+
89Kr	36	53	88.9178354(23)	3.15(4) min	β−	89Rb	3/2+
90Kr	36	54	89.9195279(20)	32.32(9) s	β−	90mRb	0+
91Kr	36	55	90.9238063(24)	8.57(4) s	β−	91Rb	5/2+
					β−, n?	90Rb
92Kr	36	56	91.9261731(29)	1.840(8) s	β− (99.97%)	92Rb	0+
					β−, n (0.0332%)	91Rb
93Kr	36	57	92.9311472(27)	1.287(10) s	β− (98.05%)	93Rb	1/2+
					β−, n (1.95%)	92Rb
94Kr	36	58	93.934140(13)	212(4) ms	β− (98.89%)	94Rb	0+
					β−, n (1.11%)	93Rb
95Kr	36	59	94.939711(20)	114(3) ms	β− (97.13%)	95Rb	1/2+
					β−, n (2.87%)	94Rb
					β−, 2n?	93Rb
95mKr	195.5(3) keV			1.582(22) μs	IT	95Kr	(7/2+)
96Kr	36	60	95.942998(62)[7]	80(8) ms	β− (96.3%)	96Rb	0+
					β−, n (3.7%)	95Rb
97Kr	36	61	96.94909(14)	62.2(32) ms	β− (93.3%)	97Rb	3/2+#
					β−, n (6.7%)	96Rb
					β−, 2n?	95Rb
98Kr	36	62	97.95264(32)#	42.8(36) ms	β− (93.0%)	98Rb	0+
					β−, n (7.0%)	97Rb
					β−, 2n?	96Rb
99Kr	36	63	98.95878(43)#	40(11) ms	β− (89%)	99Rb	5/2−#
					β−, n (11%)	98Rb
					β−, 2n?	97Rb
100Kr	36	64	99.96300(43)#	12(8) ms	β−	100Rb	0+
					β−, n?	99Rb
					β−, 2n?	98Rb
101Kr	36	65	100.96932(54)#	9# ms [>400 ns]	β−?	101Rb	5/2+#
					β−, n?	100Rb
					β−, 2n?	99Rb
102Kr[8]	36	66					0+
103Kr[9]	36	67
This table header & footer: view

1. ^mKr – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Bold half-life – nearly stable, half-life longer than age of universe.
5. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
6. Modes of decay:

   n:	Neutron emission

7. Bold italics symbol as daughter – Daughter product is nearly stable.
8. Bold symbol as daughter – Daughter product is stable.
9. ( ) spin value – Indicates spin with weak assignment arguments.
10. Primordial radionuclide
11. Used to date groundwater
12. Fission product
13. Formerly used to define the meter
14. Believed to decay by β⁻β⁻ to ⁸⁶Sr

• The isotopic composition refers to that in air.

Notable isotopes

Krypton-81

Krypton-81 (half-life 230,000 years) is useful in determining how old the water beneath the ground is. Radioactive krypton-81 is the product of spallation reactions with cosmic rays striking gases present in the Earth atmosphere, along with the six stable or nearly stable krypton isotopes.^[10] The long half-life ensures that the isotope has a uniform concentration in the atmosphere and in surface water; when the water goes underground is supply is no longer replenished and decays, allowing dating of the residence time in deep aquifers in a range of 20,000 to a million years. The same long half-life renders detection of its decay impossible and, therefore, demands some form of mass spectrometry; even so, technical limitations of the method have traditionally required the sampling of very large volumes of water: several hundred liters or a few cubic meters of water (about a milligram of krypton). This is particularly challenging for dating pore water in deep clay aquitards with very low hydraulic conductivity.^[11]

More recently, it has been announced^[12] that samples an order of magnitude less can be used successfully.

The short-lived isomer (13 sec.) krypton-81m has medical uses but is often considered impracticable as it must be generated from the rare rubidium-81. It almost entirely decays to the ground state with a monochromatic gamma ray.

Krypton-85

Main article: Krypton-85

Krypton-85 (half-life 10.728 years) is produced by the nuclear fission of uranium and plutonium in nuclear weapons testing and in nuclear reactors, as well as by cosmic rays. An important goal of the Limited Nuclear Test Ban Treaty of 1963 was to eliminate the release of such radioisotopes into the atmosphere, and since 1963 much of that krypton-85 has had time to decay. However, it is almost inevitable that krypton-85 is released during the reprocessing of fuel rods from nuclear reactors,^[13] which is far larger-volume than was ever nuclear testing.

Atmospheric concentration

See also: Nuclear reprocessing

The atmospheric concentration of krypton-85 around the North Pole is about 30 percent higher than that at the South Pole because nearly all of the world's nuclear reactors and all of its major nuclear reprocessing plants are located in the northern hemisphere, well north of the equator^[14] and transfer of air between the hemispheres is slow.

The nuclear reprocessing plants with significant capacities are located in the United States, the United Kingdom, the French Republic, the Russian Federation, Mainland China (PRC), Japan, India, and Pakistan.

Krypton-86

Krypton-86 was formerly used to define the meter from 1960 until 1983, when the definition of the meter was based on the wavelength of the 606 nm (orange) spectral line of a krypton-86 atom.^[15]

See also

Daughter products other than krypton

• Isotopes of rubidium
• Isotopes of bromine
• Isotopes of selenium